# Number of moles of molecules.

How many number of moles of molecules are there in 1 mol dm-3 of HCl?

Is it correct to find it this way?
Number of moles of HCl = 1 mol
Number of moles of H2O = 1000/18 = 55.6 mol
So, total number of moles = 55.6 + 1 = 56.6 moles

If i change the question of 3 mol dm-3 of HNO3,
Then the total number of moles of molecules will be
3+ 55.6 = 58.6 moles?

Thanks.

symbolipoint
Homework Helper
Gold Member
The general conversion is with ratios, not with sums.

If Y = cubic decimeters of substance, F = formula weight or molecular weight of sought substance, and Z = ratio of moles of sought substance to volume of sample in cubic decimeters, then molesOfSoughtSubstance = Z*Y.

Check the units carefully for that formula to see how it works. Notice you would not need "F" because it was not directly needed. You would possibly need the formula weight if you were interested in any relation between mass and moles, but in your examples, you already had number of moles of a sought compound in a given unit of volume.

Borek
Mentor
1 mol dm-3 of HCl

I have no idea what you mean. mol dm-3 is a measure of concentration, not amount.